Perfluoro dinitriles



Patented May 29,1951

PERFLUORO DINITRILES Earl T. McBee, West Lafayette, and Park A. Wiscman, Muncie, Ind., assignors to Purdue Research Foundation, La Fayette, Ind.,' a corporation of Indiana No Drawing. Original application June 30, 1946, Serial No. 687,225. Divided and this application October 6, 1949, Serial No. 119,994

3 Claims. (Cl. 260-4653) The present invention relates to difiuoromethylene compounds. More specifically, the invention relates to certain derivatives of perfiuorodicarboxylic acids having the formula:

wherein a: is an integer from two to four, inclusive.

ent invention is concerned are allrelated, being members of the series embodying the following general structure:

wherein a: is an integer from two to four, inclusive, This structure may also exist in the form NE C--(CF2) a.C' -N.

The compounds of the present invention may be prepared from the same parent compounds, the perfluorodicarboxylic acids. The preferred embodiment of the invention resides in members of the series of compounds embodying the abovegeneral structure and is inclusive of the following related types:

(1) Amides of the general formula H2N-CO-(CF2)1-CO--NH2 (2) Nitriles of the general formula e H NEC(CF2) :LCE N (3) Amines of the general formula where R. is a hydrocarbon radical; and acid or quaternary salts thereof.

(4) Acylamines of the general formula represents the residue of a monoor dicarboxylic acid, and I (5) Dihydrazides of the general formula H2N-NHC'O(CF2) rCONH NI-i 2 In all of the above formulae, .1: represents an integer from two to four, inclusive.

It is an object of thepresent invention to provide new compounds which are useful as chemical intermediates.

The compounds, in general, may be prepared from the corresponding perfluorodicarboxylic The group of compounds with which the presacid. Thus, we first prepare a diester of the selected dicarboxylic acid, for example, the diethyl ester of perfiuoroglutaric acid, having the formula C2H5OCO-(CF2) 3OCO'C'2H5, by treatment of the acid with the selected alcohol in the presence of a small amount of hydrochloric acid catalyst. After a considerable reflux period, e. g.,

10 to 20 hours, excess alcohol is removed and thediester, usually a high-boiling liquid, is recovered. The diester may then be used to prepare the diamide. l

The selected diester of the chosen perfiuorodicarboxylic acid is introduced, with a suitable organic solvent, e. g., diethyl ether, into apparatus fitted with a gas inlet, and. thesolution is treated at low temperatures, preferably at about zero degrees centigrade, with anhydrous gaseous ammonia. Sufficient ammonia to convert the ester to the diamide is bubbled into the reaction mixture. The diamide usually separates as a white solid. 7

The diamide may then be thoroughly admixed with an excess of phosphorus pentoxide, and the mixture heated until the dinitrile distills from the reaction container.

To prepare the diacyl derivatives of the diamines, the following procedure may be employed: The perfluoro nitrile, the selected acid or acid anhydride, such as acetic acid or propionic anhydride, a small amount of platinum oxide catalyst, and an organic solvent, e. g., ethyl ether, are introduced into a pressure hydrogenator. Hydrogen is introduced until a suitable pressure, e. g. 1000 p. s. i., is attained; the bomb is heated to about degrees centigrade and maintained at this temperature for a suitable period, e. g., about one hour. After cooling slowly to room temperature and preferably with agitation, the excess hydrogen is allowed to escape. The diacyl derivative of the diamine is usually separated from the hydrogenator as a crude slurry, which may be recrystallised from an organic solvent such as benzene, alcohol, or mixtures thereof. The acyl derivatives prepared in this manner are usually white crystalline solids, having a definite melting point after recrystallisation.

Representative acylamines'which may be prepared in this manner include the diacetyl, dipropionyl, 'dibutyryl, diisobutyryl, divaleryl, dicapronyl, distearyl and many other acyl derivatives of the diamines.

Salts of the diamines having the general formula N-CH2(CF2)J, -CH2-N==, wherein :n is an integer from two to four, inclusive, may be prepared by treatment of the corresponding .diamine diacyl derivative with a selected acid. The hydrolysis product, thediamine hydrochloride, sulphate, et cetera,is usually a crystalline solid after recrystallisation from ethyl ether. The salts of the diamine may be varied widely, and may be the hydrochloride, hydrobromide, sulphate, citrate, tartrate, acetate, et cetera, de: pending upon the acid used for the hydrolysis of the acyl derivative.

The free basic diamine may be prepared from the salts thereof by treatment with a base, such as dilute sodium hydroxide solution. The basic solution may be extracted with ether or other suitable organic solvent. The extract is dried, filtered, and the solvent removed. The amine remains as a heavy oil or a crystalline solid and may be purified by distillation under reduced pressure. The pure amine is usually a stable solid with a definite melting point.

Salts of other acids and quaternary salts may be prepared from the free base, by treatment with the selected acid, alkyl halide, or arylsulfonic ester. Thus, besides acid salts, may be produced the methobromide, ethochloride, ethyl (paratoluene) sulfonate, et cetera.

Within the scope of the present invention are included amines of the formulae wherein an is an integer from two to four, inclusive, and wherein R represents various hydrocarbon radicals. These compounds may be prepared by reaction of the selected alkyl halide with the primary or secondary amine at moderately elevated temperatures, by which method the hydrohalide salt of the secondary or tertiary amine is produced. The free base may then be liberated by treatment of the salt with a moderately strong basic solution. Representative secondary and tertiary amines are By the reaction of a selected diester of a perfiuorodicarboxylic acid and hydrazine hydrate may be produced the corresponding dihydrazide. The dihydrazide is formed as a white, crystalline solid and may be recrystallised from water.

Several perfluorodicarboxylic acids from which members of this new group of compounds may be produced and methods for their preparation are disclosed in our applications Serial No. 625,108, filed October 2'7, 1945, now Patent 2,453,146, and Serial No. 633,542, filed December '7, 1945, now abandoned. Other perfluorodicarboxylic acids may be prepared by the same methods and in the following manner:

(a) 1,1-dichloro-2,2-difluoroethylene is dimerized at about 200 degrees centigrade to yield 1,1,2,2-tetrachloro-3,3,4,4-tetrafiuorocyclobutane, boiling at about 131 degrees centigrade.

(b) The cyclobutane is dehalogenated with zinc to give 1,2-dich1oro-3,3,4,4+tetrafluorocyclobutane, boiling at about 66 degrees centigrade.

(c) The cyclobutene is oxidised, e. g., withpotassium permanganate, to perfluorosuccinic acid, HOOC(CF2)2COOH, having a boiling point of about 120 degrees centigrade. Further disclosure of this process may be obtained from the I. G. Farbenindustrie Research Reports of the Frank- 4 furt-Hochst works for 1943, Microfilm Number 6 of 1943 material.

Further disclosure of esters of perfluoroadipic acid, which are useful in the preparation of some of the compounds of the present invention is found in our application Serial No. 687,226, filed July 30, 1946, now Patent 2,453,147.

The compounds of the present invention possess the structure:

wherein a: is an integer from two to four, inclusive. The preferred embodiment of the invention resides in those compounds which possess the above-general structure and which are selected from the group consisting of diamides, dinitriles, di(acylamines), dihydrazides, diamines and salts of diamines.

Ewample 1.Diamide of perfluoroadipic acid Fifty grams 'of the diethyl ester of perfiuoroadipic acid, prepared by the condensation of perfiuoroadipic acid (as disclosed in our application Serial No. 625,108, filed October 27, 1945, now Patent 2,453,146) and ethanol in the presence of hydrochloric acid, and boiling at 70.0 to 71.0 degrees centigrade at 2-3 millimeters of mercury pressure absolute, was introduced with 200 milliliters of anhydrous ethyl other into a one-liter, threeneck flask fitted with reflux condenser, thermometer and a gas inlet. Anhydrous gaseous ammonia was bubbled through the solution at zero degrees centigrade as long as it was absorbed, and the diamide separated. The solvent was removed by evaporation, leaving 41 grams of a white product. A sample of the material melted at 237 degrees centigrade, uncorrected, and no change in the melting point occurred upon recrystallization from benzene. Analysis:

Fluorine Content Found, Percent PerCc'nt Diamide of periluoroadipic acid, 111N00- (CF2)4CONH2 54. 1 52. 9

Example 2.Perfluoroadiponitrile reaction flask. The product, perfiuoroadiponitrile, boils at about 63 degrees centigrade, is

water-insoluble, and possesses little odor. The vapors of the product, however, appear to be nauseating and to have an adverse efiect upon the respiratory system. Analysis:

Fluorine Content Example 3.Diacetyl derivative of 2,2,3,3,4,4,5,5'- octafluoro-I,6-hexanediamine Twenty grams of pe'rfluoroadiponitrile, 25 grams of acetic anhydride, one gram of platinum oxide catalyst and 100 milliliters of anhydrous ethyl ether were added to a 500-milliliter Parr bomb hydrogenator. Hydrogen was introduced until a pressure of 1000 p. s. i. was obtained. The sealed bomb was heated rapidly, with shaking, to 100 degrees centigrade, maintained at this temperature for one hour and allowed to cool slowly, with shaking, to room temperature. The excess hydrogen was allowed to escape from the cooled bomb, and the gray slurry which comprised the reaction product was placed in ice-water. Thirty grams of gray solid was collected and recrystallised from benzene and alcohol. The" resulting white product weighed grams and, after repeated recrystallisations from benzene-alcohol and alcohol-water solutions, melted sharply at 180-181 degrees centigrade. Analysis:

Fluorine Content Calculaterl, Per Cent Found, Per Cent Diacetyl derivative of 2,2,3,3,4 4,5,5-octafluororehexaneaiamm onsoori CH2-(CF3)4 CHz-NHCO 0H3 Ewample 4.--2,2,3,3,4,4,5,5-octafluor0 i,6-

hewanediamine salts Fluorine Content Calculated, Per Cent Found, Per Cent 4 4, 5,5 Octafluoro-1,6-hexsnediamine 'sulp te,HzN-CHz-(CFah-CHz-NHz.H1804. 41.5 42.4

The amine sulfate from the above example was dissolved in sodium hydroxide solutiongextracted with ethyl ether, and hydrogen chloride was passed into the dry extract. The hydrochloride separated and was collected.

The diamine hydrochloride prepared as above melted above 250 degrees centigrade. Analysis:

Per Cent Chlorine Per Cent Fluorine Fd. Oalcd Fd. Calcd 2,2,3,3,4,4,5,5-Octafluoro-l,fi-hexanediamine Hydrochlonde, HnN CHr- (CF2)4 CH:- NHmHCl Example 5.--2,2,3,3,4,4,5,5-octafluoro-1,6-

hexanediamine Fourteen grams of the diacetyl derivative of 2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediamine, 250 grams of water and 62 grams of concentrated sulfuric acid were added to a 500-milliliter roundbottom flask fitted with a reflux condenser. The resilient mixture was refluxed for 18 hours, al-' though the hydrolysis occurred quite readily and in a shorter time than the total reflux period. The reaction product was cooled, whereupon a crystalline white solid separated. This product, weighing 15 grams after drying, was assumed to be the monosulfate of 2,2,3,3,4,4,5,5-octafluoro- 1,6-hexanediamine.

The sulfate was placed in 200 milliliters of water and dilute sodium hydroxide solution was added slowly until the solution was slightly basic. As the sodium hydroxide was added, the sulfate dissolved and a dark red oil separated. The basic solution was extracted with three -millilter portions of ethyl ether. The ether extract was dried over calcium sulfate, filtered, and the ether evaporated. A light brown liquid which crystallised upon standing remained. The solid possessed an amine-like odor.

The impure amine was distilled under reduced pressure and 5.5 grams of white crystalline product, boiling at 65-66 degrees centigrade at 5-6 millimeters of mercury pressure absolute, was collected. .The solid melted at 44-45 degrees centigrade and was unusually stable to light and air. Analysis:

Fluorine Content Calcu- Found lated, Per cent Per Cent 2,2,3,3,4,4,5,5- O ctafluoro -l,6-hexanediamine,

H2NH2C(CF2)4CH2NH2 59. 2 53. 5

Example 6.-Diamz'cle of perfluoroglutaric acid Fluorine Content 62%tfitt tt'tftfiii fi.ifgi i 3s. 7 38.5 Diamide (6f perfluoroglutaric acid NHi( orm-iiNH, 49.4 47.9

Example 7.Perfluoroglutaronitrile Phosphorus pentoxide (225 grams) and 96 grams of the diamide of perfluoroglutaric acid were added to a round-bottom distilling flask of 500 milliliters capacity. The reactants were mixed thoroughly, whereafter the flask and contents were immersed in an oil bath at -200 degrees centigrade for four hours. The oil bath was then removed and further heating continued with a Bunsen burner. The colorless liquid Fluorine Content Example 8. 2,2,3,3,4,4-hemafluoro-1,5-pentanediamine Fifty grams of powdered perfluoroglutaric acid diamide and 225 grams of phosphorus pentoxide were added to a one-liter, round-bottom, distilling flask and the reactants 'mixed intimately. The resultant mixture was heated'witha Tirril burner and the distillate condensed in an icewater-cooled receiver.

A second experiment, identical with that just described, was performed. The combined prodnot from the two experiments weighed 63 grams, and, when distilled at atmospheric pressure, yielded 24 grams of perfiuoroglutaronitrile and 32 grams believed to be perfiuoroglutarimide, boiling at 155-159 degrees centigrade, which was formed by the splitting of ammonia from perfiuoroglutaramide.

Twenty-four grams of perfluoroglutaronitrile, 1 gram of platinum oxide catalyst, 25 grams of acetic anhydride, and sufficient ethyl ether to give a volume of 150 milliliters were introduced into a Parr bomb. Hydrogen was then introduced until a pressure of 1000 p. s. i. was attained. The sealed bomb was heated with shaking to 110 degrees centigrade, cooled slowly to 60 degrees centigrade and allowed to remain at this temperature under 1000 p. s. i. hydrogen pressure overnight. It was thereafter cooled to room temperature and the excess hydrogen bled therefrom. The reaction product was filtered to remove excess catalyst, and the filtrate evaporated slowly. The remaining oily product was poured into 400 milliliters of 20 percent sulfuric acid solution, and the resulting mixture was refluxed overnight. The hydrolysis product was cooled to room temperature, decolorized with activated carbon, filtered, made alkaline with sodium hydroxide solution, and the basic solution extracted with four 100-milliliter portions of ethyl ether. The extract was dried over calcium sulfate, filtered, and distilled. A red oil with an amine-like odor remained in the flask. This was identified as 2,2,3,3,4,4-hexafiuoro-1,5r pentanediamine.

Example 9.-Dihydmzide of perfluoroadipic acid Ten milliliters (14 grams; 0.04 mole) of the diethyl ester of perfluoroadipic acid, milliliters of absolute ethyl alcohol and 20 milliliters of 42 percent hydrazine hydrate in water were mixed together at room temperature. The white, crystalline hydrazide formed in about twenty minutes and was suction filtered, washed with dry ether and recrystallised from boiling water. The yield was 9 grams (76 percent of theory); melting point 186 to 187 degrees centigrade.

This application is a division of our application Serial No. 687,225, filed July 30, 1946, which is Patent 2,515,246, granted July 18, 1950.

We claim:

1. A 'dinitrile having the general formula NEC(.CF2)1 CEN wherein a: is an integer from 2 to 4, inclusive.

2. Perfluoroadiponitrile, NEC(CF2)4CEN. 3. Perfiuoroglutaronitrile,

NEC(CF2)3CEN EARL T. McBEE. PARK A. WISEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,422,528 Cass et a1 June 17, 1947 2,426,224 Kharasch Aug. 26, 1947 OTHER REFERENCES Henne et al.: J. Am. Chem. Soc., vol. 67, pp. 1235-1237 (1945). 

1. A DINITRILE HAVING THE GENERAL FORMULA 